Many articles and particularly vehicles are painted so as to improve the appearance as well as protect same from corrosion. These vehicles are generally spray painted to quickly and efficiently apply the paint to the body of the vehicle.
Such paint is applied onto the body of the vehicle during the original equipment manufacture (O.E.M.) where the paint is baked on. However paint is also required to be sprayed when the vehicle requires auto body repair, or to refinish same.
A variety of paints and paint formulations have heretofore been utilized in finishing articles and particularly finishing or refinishing automobile bodies, including urethane paints which are utilized to refinish vehicle bodies.
For example, U.S. Pat. No. 3,832,217 relates to a process for forming exterior finish coating films for automotive bodies which utilize a thermosetting resin and includes the use of CAB in melamine formulated paints that are baked in O.E.M. applications. Moreover, other O.E.M. baking systems that include CAB in paints having melamine formulations are examined in Polym. Paint Col. J. 1979, vol. 169 No. 4010, 986. The CAB mentioned in the above identified prior art is used to control the metallic flake orientation.
Finally, Japanese patent No. 88-327509/46 teaches the formation of coating with metallic lustre with the addition of CAB in a resin having an acid number under 10.
It is not uncommon for defects in the form of craters or mounds to develop on the surface of paints, and particularly on the surface of urethane paints, during the course of drying. Craters or dimples are depressions which visually form on the surface or film of the paint during drying. Mounds, on the other hand, are visible protrusions or hills which form on the surface or film of the paint during drying. Such defects often develop on the surface of medium to high solids two-component urethane paints whether clearcoat or single stage. Medium to high solids two-component urethane paints generally have a solids content of between 40% to 70% solids by weight when ready to spray. In other words the volatiles will have a weight content of 60% to 30% respectively. The volatiles will evaporate. The solid content or level is measured as defined in ASTM 2369.
It is an object of this invention to minimize the formation of craters or mounds on the surface of said paint, and particularly to minimize the formation of those defects on the surface of sprayed urethane paint by adding a low concentration of CAB.
It is another object of this invention to provide for an improved method of spraying urethane paints so as to minimize the formation of surface defects during drying.
The broadest aspect of this invention relates to a coating composition having a concentration of cellulose acetate butyrate of between 0.1% and 2.0% by weight of cellulose acetate butyrate to the total weight of solids in said coating, said cellulose acetate butyrate having a viscosity equal to or greater than 0.5 seconds, and less than 20 seconds so as to minimize the formation of craters and mounds on the surface of the coating when dried at ambient temperature.
Another aspect of this invention relates to a urethane paint for spraying said pain having a concentration of cellulose acetate butyrate of between 0.1% and 2.0% by weight of cellulose acetate butyrate to the total weight of solids in said ready-to-spray paint, said cellulose acetate butyrate having a butyryl content of approximately 38% and acetyl content of approximately 13.5%, and having a viscosity equal to or greater than 0.5 seconds, and less than or equal to 2 seconds so as to minimize the formation of craters and mounds on the surface of said paint when dried at ambient temperature.
Yet another aspect of this invention relates to the method of spraying an article with urethane paint comprising the steps of: adding cellulose acetate butyrate to said urethane paint; said cellulose acetate butyrate having a viscosity equal to or greater than 0.5 seconds and less than 20 seconds; spraying said article; drying said sprayed article at ambient temperatures; where said cellulose acetate butyrate is selected to have a concentration between 0.1 and 2.0% by weight of the total weight of solids in said paint ready for spraying.